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(11) | EP 2 472 065 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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Damper coverplate and sealing arrangement for turbine bucket shank Dämpferabdeckplatte und Dichtungsanordnung für einen Turbinenschaufelschaft Couverture d'amortisseur et étanchéité pour aube de turbine |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to turbomachines and particularly, to damper pins and seal pins disposed between adjacent buckets on a rotor wheel.
[0002] As is well known, turbines generally include a rotor comprised of a plurality of rotor wheels, each of which mounts a plurality of circumferentially-spaced buckets. The buckets each typically include an airfoil, a platform, a shank and a dovetail, the dovetail being received in mating dovetail slot in the turbine wheel. The airfoils project into a hot gas path downstream of the turbine combustors and convert kinetic energy into rotational, mechanical energy. During engine operation, vibrations are introduced into the turbine buckets and if not dissipated, can cause premature failure of the buckets.
[0003] Many different forms of vibration dampers have been proposed to minimize or eliminate vibrations. Vibration dampers are often in the form of an elongated damper pins that fit between adjacent buckets and provide the damping function by absorbing harmonic stimuli energy produced as a result of changing aerodynamic loading. A damper pin is typically retained in a groove formed along one circumferentially-oriented "slash face" in the turbine blade shank region of one of each pair of adjacent buckets. The damping pin is centrifugally loaded during operation and, in order to prevent bucket-to-bucket binding, the groove must be machined so as to allow the pin to float relatively freely within the groove. At the same time, highly-compressed air is often extracted from the compressor of an axial turbine for the purpose of cooling turbine components, particularly those in the hot gas path downstream of the combustion. This cooling air is required to maintain the temperature of the turbine components at an acceptable level for operation, but comes at a cost to overall turbine efficiency and output. Any of the cooling flow that leaks out of the turbine components is essentially wasted. The pocket created by a damper pin groove provides a large leakage path for cooling flow to escape from the bucket shank region. The cooling efficiency can also be impaired by ingress of hot gas from the hot gas path into the bucket shank region.
[0004] In one prior arrangement, the damper pin has reduced-cross-section ends supported on shoulders formed in the bucket shank, with annular seals at the interfaces between the reduced-cross-section ends and the main body portion of the pin to minimize leakage along the damper pin groove.
[0005] For industrial gas turbines utilizing long bucket shank designs, a further approach to seal against cross-shank leakage is to provide radial seal pins between the shanks of adjacent buckets on the fore and aft sides of the shank, below the axially-extending damper pin. Like the damper pin, the radial seal pins are seated in seal pin grooves formed on the same slash face as the damper pin groove, and engage the substantially flat sides of the shank of the adjacent bucket. The sealing effectiveness of these cross-shank seals is an important factor in increasing the bucket life by minimizing thermal stress. Even when using both damper pins and radial seal pins, however, gaps remain between the radial seal pins and the reduced-cross-section ends of the axially-oriented damper pin, again creating readily-available leakage paths for hot combustion gases flowing past the buckets.
[0006] US 4872812 describes a gas turbine rotor blade platform sealing and damping system having elongated symmetrical insert elements of equilateral triangular cross-section loosely received within complementary shaped pockets at the spacing gaps between opposing convex and concave airfoil side edges of adjacently mounted blade platforms.
[0007] US 6273683 describes a rotating blade group for a turbo-machine wherein the gap between adjacent blades is sealed by a seal pin, its central portion 110 and by a seal plate at each of the front and rear portions. The seal plates are inserted into corresponding grooves formed in the adjacent edges of adjoining blades and held in place by end plates. The end of the seal plates may be chamfered to improve the seal against the end plate
[0008] It would therefore be desirable to provide a more reliable sealing feature in order to prevent, minimize or control the escape of cooling flow from a pressurized shank cavity, prevent or minimize flow from leaking across the turbine blade from the forward wheel space to the aft wheel space in the case of a non-pressurized shank cavity, and/or to prevent ingress of hot gas path air into the shank region.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention resides in a bucket for a turbine machine rotor wheel comprising an airfoil portion, a shank portion and a dovetail mounting portion, the shank portion including opposite side faces, one of the side faces formed with an axially-oriented slot extending between forward and aft ends of the shank portion; an elongated damper pin of uniform cross-section seated in the axially oriented slot, the elongated damper pin formed with axially slanted forward and aft ends that rest on similarly slanted surfaces formed internally of the shank portion at opposite forward and aft ends thereof.
[0010] The invention also resides in a bucket pair in a turbomachine comprising a first bucket and a second adjacent bucket as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiment of the present invention will now be described, by way of example only, with reference to the accompany drawings in which:
Fig. 1 is a perspective view of a gas turbine bucket and damper pin assembly;
Fig. 2 is a partial side elevation showing a pair of circumferentially-adjacent buckets with a damper pin located therebetween;
Fig. 3 is a partial perspective view of another gas turbine bucket and damper pin assembly, wherein the damper pin is provided with discreet seal elements in one prior arrangement;
Fig. 4 is a perspective view of a damper pin with attached discreet seal elements of the type shown in Fig. 3;
Fig. 5 is a partial end view of a pair of adjacent buckets incorporating a damper pin/seal of the type shown in Figs. 3 and 4;
Fig. 6 is a partial side elevation of a damper pin and radial seal pin configuration in accordance with a first exemplary but nonlimiting embodiment of this invention;
Fig. 7 is a partial end view of a pair of adjacent buckets incorporating the damper pin and radial seal pin arrangement of Fig. 6;
Fig. 8 is a partial perspective view of the turbine shank portion on which the damper pin rests; and
Fig. 9 is a partial side elevation of a bucket incorporating a damper pin and radial seal pin configuration in accordance with another exemplary but nonlimiting embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Figs. 1 and 2 illustrate a conventional bucket 10 including an airfoil 12, a platform 14, a shank 16 and a dovetail 17. The dovetail 17 is utilized to secure the bucket 10 to the periphery of the rotor wheel (not shown), as is well understood in the art. A damper pin 20 is located along one axial edge (or slash face) 22 adjacent (i.e., radially inward of) the bucket platform 14 with the leading end 24 of the damper pin 20 located nearer the leading edge of the bucket, and the trailing end 26 of the damper pin located nearer the trailing edge of the bucket.
[0014] It will be appreciated that a similar pin 20 is located between each adjacent pair of buckets 18, 118 on the turbine wheel, as apparent from Fig. 2. Specifically, the damper pin 20 is located in a groove or slot 28 extending along the entire slash face 22 of the bucket 118. The damper pin 20 includes a substantially cylindrical body portion 30 between a pair of substantially semi-cylindrical, opposite ends 24, 26 interfacing at shoulders 39. This configuration creates flat support surfaces 32, 34 (best seen in Fig. 1) that are adapted to rest on the machined bucket platform surfaces or shoulders (one shown at 36 in Fig. 2) at opposite ends of the groove 28 formed in the bucket slash face, thereby providing good support for the pin while preventing undesirable excessive rotation during machine operation.
[0015] Figs. 3 and 4 illustrate a long bucket 37 where radially-oriented seal pins 38, 40 are used in combination with a damper pin 42. In this instance, the damper pin 42 is formed or provided with "piston ring" seals 44, 46 at opposite ends where the damper pin transitions to reduced-cross-section ends 48, 50. Note, however, that there is still a considerable gap between the radially outer ends 52, 54 of the seal pins 38, 40 and the ends 48, 50 of the damper pin 42. In addition, as made clear from Fig.5 (where the reduced-cross-section end 48 is visible between adjacent buckets 37, 137) the slot in which the damper pin is located is open at both ends, allowing cooling air to escape through the clearance spaces between the pin and the groove in which it is seated, especially along the reduced-cross-section ends 48, 50.
[0016] It should be understood that the grooves in which the damper pin 42 and radial seal pins 38, 40 are seated are provided on only one side of the bucket, and that they engage flat surfaces on an adjacent bucket. In other words, each bucket in a circumferential row of buckets is formed such that the damper/seal pins seated in grooves formed on one side of a bucket engage flat surfaces of an opposite side of an adjacent bucket.
[0017] Fig. 6 illustrates a bucket 56 provided damper pin/radial seal pin configuration in accordance with an exemplary but nonlimiting embodiment of the invention. Specifically, an axially-extending, substantially round damper pin 58 is formed with slanted forward and aft ends defined by, for example 45° surfaces 60, 62 that rest on similarly slanted surfaces 64, 66 formed internally of the shank, at opposite forward and aft ends thereof. More specifically, surfaces 60, 62 are slanted in opposite linear or axial directions. This design eliminates the need for the reduced-cross-section ends and the "piston ring" seals as shown in Fig. 4, and allows the length of the damper pin 58 to be shortened. The slanted ends or surfaces 60, 62 also allow the radial seal pins 68, 70 to be extended in length in a radially outward direction to close the gap between the radial seal pins and the damper pin. For example, in one exemplary embodiment, the radial pin seal slots or grooves 72, 74 in the shank may be extended radially outwardly (toward the airfoil) by 1.56mm (0.140 inch), to obtain greater sealing performance. Note also that the upper or radially outer ends of the seal pin slots or grooves 72, 74 are at least partially overlapped by the slanted end surfaces 60, 62 of the damper pin 58. This arrangement also allows additional shank material to be retained at the ends of the damper pin groove surfaces 62, 64 to substantially cover the ends of the damper pin 58 as shown in Figs. 7 and 8, further reducing the area of the leakage path. In one example, the thickness of the shank from the edge of the damper pin 58 to the forward face 72 of the shank may be on the order of 8.13mm (0.320 inch), thus providing sufficient material for the "cover plates" 75 (Fig. 7). A comparison of the buckets 76, 176 in Fig. 7 illustrates the significant reduction is leakage area resulting from the addition of the cover plates 75. Thus, there are two aspects of the exemplary design that reduce leakage at each of the forward and aft ends of each pair of adjacent buckets. First, the gap between the upper end of the radial pin 68 and the damper pin 58 (as defined by the solid ligament or web 76) can be reduced, and second, an increase in shank material at the opposite ends of the damper pin groove 78 enables the ends of the damper pin 58 to be substantially covered by the cover plates 75.
[0018] In another exemplary but nonlimiting example shown in Fig. 9, the forward side radial pin 80 may be shortened in length and angled more sharply toward the damper pin 82, allowing the outer end of the radial seal pin 80 to be located further up the slanted surface of the damper pin 82 to reduce the leakage area between the damper pin and seal pin. Because pressures are greater at the radially outer end of the forward side shank portion, leakage is more likely in this area than in radially inner areas of the shank.
[0019] For both described embodiments, the radially outer edges of the seal pin grooves (one referenced by numeral 84 in Fig.8) are shown to be substantially parallel to the slanted surface of the damper pin groove (one referenced by numeral 86 in Fig. 8). It will be understood, however that these surfaces need not be parallel. The angle of edge 84 is the contact angle for the radial pin, and that angle may be optimized depending on various parameters including the loading on the pin under various operating conditions, diameter of the pin, etc. In addition, the dimensions for the damper pin and seal pin grooves, the diameter and length dimensions of the damper pin and seal pins will also be application specific, also taking into account thermal growth characteristics; damper pin-to-bucket mass ratio to insure effective vibration damping; and other parameters understood by those skilled in the art.
[0020] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
an airfoil portion (12), a shank portion (16) and a dovetail mounting portion (17), said shank portion including opposite side faces, one of said side faces formed with an axially-oriented slot (28) extending between forward and aft ends of said shank portion; an elongated damper pin (58) of uniform cross-section seated in said axially oriented slot (28), said elongated damper pin formed with axially slanted forward and aft ends (60, 62) that rest on similarly slanted surfaces (64, 66) formed internally of the shank portion (16) at opposite forward and aft ends thereof.
a first bucket (56) and a second adjacent bucket (56), each bucket as recited in any of claims 1 to 8, the shank of the second bucket (176) being adjacent the shank (16) of the first bucket (76).
einen aerodynamischen Schaufelprofilabschnitt (12), einen Schaftabschnitt (16) und einen Schwalbenschwanzbefestigungsabschnitt (17), wobei der Schaftabschnitt gegenüberliegende Seitenflächen enthält, wobei sich eine der Seitenflächen, die mit einem axial orientierten Schlitz (28) gebildet ist, zwischen den vorderen und hinteren Enden des Schaftabschnitts erstreckt; einen langgestreckten Dämpferstift (58) von gleichmäßigem Querschnitt, der in dem axial orientierten Schlitz (28) sitzt, wobei der langgestreckte Dämpferstift mit axial geneigten vorderen und hinteren Enden (60, 62) gebildet ist, die auf ähnlich geneigten Oberflächen (64, 66) ruhen, die innerhalb des Schaftabschnitts (16) auf gegenüberliegenden vorderen und hinteren Enden desselben gebildet sind.
zweiten Dichtungsstifts (68, 70) mindestens teilweise durch die geneigten Enden (60, 62) und durch den langgestreckten Dämpferstift (58) überlappt sind.
eine erste Schaufel (56) und eine zweite benachbarte Schaufel (56), wobei jede Schaufel eine solche nach einem der Ansprüche 1 bis 8 ist, wobei der Schaft der zweiten Schaufel (176) benachbart zu dem Schaft (16) der ersten Schaufel (76) ist.
une partie aérodynamique (12), une partie de queue (16) et une partie de montage en queue d'aronde (17), ladite partie de queue comprenant des faces latérales opposées, l'une desdites faces latérales étant formée avec une fente axialement orientée (28) s'étendant entre les extrémités avant et arrière de ladite partie de queue ; une broche d'amortissement allongée (58) de section transversale uniforme calée dans ladite fente axialement orientée (28), ladite broche d'amortissement allongée étant formée avec des extrémités avant et arrière axialement inclinées (60, 62) qui reposent sur des surfaces de même inclinaison (64, 66) formées à l'intérieur de la partie de queue (16) à ses extrémités avant et arrière opposées.
une première aube (56) et une seconde aube adjacente (56), chaque aube répondant à l'une quelconque des revendications 1 à 8, la queue de la seconde aube (176) étant adjacente à la queue (16) de la première aube (76).
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description